The present disclosure relates generally to the installation of roofs. More specifically, the present disclosure relates to improved techniques for lifting and positioning a dome roof on a storage tank.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Above ground storage tanks are frequently used to store industrial quantities of a variety of raw and finished materials. These storage tanks may contain liquids, gases, solids, or some combination thereof and are used in a variety of industries. For example, the oil and gas industry frequently uses above ground storage tanks to store refined hydrocarbon products. Additionally, above ground storage tanks are also common in the petrochemical, pharmaceutical, cosmetics, food, and consumer products industries.
A variety of storage tanks may be used across all industries. For example, a storage tank may be cylindrically shaped with a fixed roof. The fixed roof, as opposed to an open top storage tank (e.g., a hopper), has the benefit of minimizing evaporation of liquid product in the tank. Moreover, a fixed roof limits contamination of the stored product by keeping foreign matter (e.g., water, dust, etc.) out of the tank. Fixed roofs come in a variety of configurations including flat, coned, umbrella, domed, etc. The roof shape may be based on the intended application of the storage tank. For example, a domed roof may be better suited for higher pressure applications because the curved structure typically distributes pressure better than a flat roof.
A dome roof is one of many different kinds of roofs that may be used on storage tanks. Dome roofs are typically self-supported, spherical segment frame structures. Current methods of dome roof construction have created several challenges for the industry. Dome roofs are typically assembled on the ground, or a surface near a base of the tank (e.g., inside or outside the tank), and then lifted into position for installation. Conventional techniques for lifting a dome include positioning multiple manually operated grip hoists about a circumference of the tank, at or near a top rim of the tank. The grip hoists are coupled to the dome using couplings (e.g., chains, cables, ropes, webbing, etc.). The lifts are then manually actuated by one or more operators positioned at each lift to the dome roof from the base of the tank to the top rim of the tank. Due to manufacturing tolerances and wear, the grip hoists may operate at different rates or speeds. Accordingly, coordinating movement of the lifts can be difficult and time consuming. For example, if the lifts do not lift the dome roof at the same speed, the dome may tilt in one direction, such that the weight of the dome is not evenly distributed among the lifts. Leveling a tilted dome before installation may add time to dome installation. Further, to change each grip hoist from “lift” mode to “lower” mode may take a two-man team as long as ten minutes or more, thereby decreasing the efficiency of the installation process.